当包含返回true时如何在列表中查找元素的索引位置

Question

I've got a List of HashMap so I'm using List.contains to find out if the list contains a specified HashMap . In case it does, I want to fetch that element from the list, so How do I find out index position of where the element is?

    List benefit = new ArrayList();
    HashMap map = new HashMap();
    map.put("one", "1");
    benefit.add(map);
    HashMap map4 = new HashMap();
    map4.put("one", "1");

    System.out.println("size: " + benefit.size());
    System.out.println("does it contain orig: " + benefit.contains(map));
    System.out.println("does it contain new: " + benefit.contains(map4));

    if (benefit.contains(map4))
        //how to get index position where map4 was found in benefit list?

Answer 1

benefit.indexOf(map4)

It either returns an index or -1 if the items is not found.

I strongly recommend wrapping the map in some object and use generics if possible.

Answer 2

Here is an example:

List<String> names;
names.add("toto");
names.add("Lala");
names.add("papa");
int index = names.indexOf("papa"); // index = 2

Answer 3

indexOf(object)

get(index)

Answer 4

Use List.indexOf() . This will give you the first match when there are multiple duplicates.

Answer 5

列表#indexOf

Answer 6

int indexOf(Object o)此方法返回此列表中第一次出现指定元素的索引，如果此列表不包含此元素，则返回 -1。

Answer 7

int indexOf() can be used. It returns -1 if no matching finds